The polymerization of olefins, particularly ethylene, is well known and has been a widely practiced commercial art for many decades. Catalysts for such polymerization are well known to include Ziegler type catalysts. In the Ziegler type catalyst field, the catalyst is usually made up of a transition metal compound and an alkyl aluminum, which is used as a co-catalyst, sometimes with a magnesium compound as well, usually on a suitable support.
In more recent times, it has been discovered that the copolymerization of ethylene and higher olefins, that is the production of LLDPE, can be catalyzed by special zirconium and/or hafnium compounds. These compounds, called metallocenes, have been proposed for use in this service in combination with aluminoxanes, as co-catalysts, both deposited on a silica substrate.